According to the 3GPP standard, a subscriber can be intercepted based on Mobile Station International ISDN Number MSISDN, International Mobile Subscriber Identity IMSI and International Mobile Equipment Identity IMEI only if roaming under the Mobile Switching Centre MSC acting as interception node; or in The Gateway Mobile Switching Centre GMSC, the roaming leg can be intercepted based on IMSI and MSISDN of the B-party. The 3GPP standard does not foresee the possibility, for an MSC acting as interception node, to intercept incoming calls originated from subscribers belonging to external networks or from subscribers belonging to external nodes. Subscribers belonging to external networks/nodes are in this patent application referred to with the term “non local subscribers”.
FIG. 1 is part of the prior art and discloses an Intercept Mediation and Delivery Unit IMDU, also called Intercept Unit, that is a solution for monitoring of Interception Related Information IRI and Content of Communication CC for a target. The different parts used for interception are disclosed in current Lawful Interception standards (see 3GPP TS 33.108 and 3GPP TS 33.107—Release 7). A Law Enforcement Monitoring Facility LEMF is connected to three Mediation Functions MF, MF2 and MF3 respectively for ADMF, DF2, DF3 i.e. an Administration Function ADMF and two Delivery Functions DF2 and DF3. The Administration Function and the Delivery Functions are each one connected to the LEMF via standardized handover interfaces HI1-HI3, and connected via interfaces X1-X3 to an Intercepting Control Element ICE in a telecommunication system. Together with the delivery functions, the ADMF is used to hide from ICEs that there might be multiple activations by different Law Enforcement Agencies. Messages REQ sent from LEMF to ADMF via HI1 and from the ADMF to the network via the X1 interface comprise identities of a target that is requested to be monitored. The Delivery Function DF2 receives Intercept Related Information IRI from the network via the X2 interface. DF2 is used to distribute the IRI to relevant Law Enforcement Agencies via the HI2 interface. Intercept Related Information IRI, received by DF2 is triggered by Events that in Circuit Switching domain are either call related or non-call related. In Packet Switching domain the events are session related or session unrelated. The Delivery Function DF3 receives Content of Communication CC, i.e. speech and data, on X3 from the ICE. In Circuit Switching, DF3 is responsible for call control signaling and bearer transport for an intercepted product.
3GMS shall provide access to the intercepted Content of Communications and the Intercept Related Information of the mobile target on behalf of Law Enforcement Agencies (see 3GPP TS 33.106 “Lawful interception architecture and functions” release 6). A mobile target in a given 3GMS can be a subscriber of that 3GMS, or a user roaming from another 3GMS or from any other network capable of using that 3GMS (such as a GSM or mobile satellite). The intercepted CC and the IRI can only be delivered for activities on that given 3GMS. For interception, there needs to be a means of identifying the target, correspondent and initiator of the communication. According to standards, target identities used for interception of CS and GPRS service shall be MSISDN, IMEI and IMSI.